1. Field of the Invention
The invention relates to an andiron for supporting logs on a domestic fireplace hearth.
2. Prior Art
It is well known that open domestic fireplaces using common basket type grates to support fuel are relatively ineffective for heating a room. Common grates suspend the fuel a short distance above the hearth to increase air flow through the fuel, but such grates remove heat by conduction and set up convection currents which pass heat up the chimney. Sides of the grate also restrict radiation of heat into the room from high temperature portions of the fire.
Some mechanical devices are available to improve heat transfer to the room, one example being a double walled fireplace that circulates air into the room from spaces between the double walls to improve heat transfer, but this type of device is expensive to construct and cannot be easily incorporated into an existing fireplace. Tubular grates to support fuel and to heat air passing through the tubes into the room can be fitted into an existing fireplace, but detract from the appearance of the fireplace and also cool the fire to the detriment of combustion. It is considered that a major factor contributing to the inefficiency of common fireplaces is that most of the heat that is transfered to the room is transfered by radiation, but typically the portion transfered by radiation is only a small portion of the total heat from the fire. The remaining heat is removed from the fire by conduction and convection, most of which tends to escape up the chimney. Furthermore a portion of heat radiated from the fire is radiated to walls of the fireplace, which is then lost because convection currents cool the heated walls and pass up the chimney.
It has already been recognized that if the proportion of radiant heat transfer is increased, the heat radiated to the room will increase, thus increasing effectiveness of the fire. Andirons or grates have been designed to hold fuel so that a greater portion of heat is transfered to the room by radiation from the burning surfaces thereof, but when using some of these devices it has been found that sometimes it is difficult to maintain satisfactory combustion and effective radiation over extended periods of time.